$$\require{cancel}$$
One way to see quarks is to use the fact that we can liberate quarks for a short time, at high energy scales. One such process is $$e^+e^- \rightarrow q \bar{q}$$, which use the fact that a photon can couple directly to $$q\bar{q}$$. The quarks don’t live very long and decay by producing a “jet” a shower of particles that results from the decay of the quarks. These are all “hadrons”, mesons and baryons, since they must couple through the strong interaction. By determining the energy in each if the two jets we can discover the energy of the initial quarks, and see whether QCD makes sense.